Touchpad input devices are small, touch-sensitive devices that can be used to replace the mouse cursor locator/input device in mouse-driven personal computers. The touchpad typically includes a small touch-sensitive screen anywhere from one by two inches up to three by five inches; the touchpad output is an analog signal representative of the location of the touching device on its surface. The computer system employs this information in placing the cursor on the CRT display. Touchpads may be used as absolute cursor location devices in which the cursor is placed in the same relative location as that of the touch device on the touchpad screen. When used as an absolute positioning device, however, the touchpads make precise cursor location difficult due to the small screen size.
Touchpads are more typically used as relative cursor positioning devices in which the cursor is moved across the display using one or more strokes of the touchpad surface; the cursor movement is related in some manner to the movement of the touchpad device across the surface. However, in order to move the cursor long distances, multiple strokes of the touchpad surface are required. In the smaller touchpads, the problems associated with multiple strokes are magnified due to the short maximum stroke distance.
Touchpad devices typically include a switch or "button" on the lower side of the pad which, when pressed, is used to emulate the selection function of the button on a mouse. When the operator desires to "drag" the cursor across the display, the button must be held down. When the cursor must be moved relatively long distances, necessitating multiple touchpad strokes, it is difficult or impossible to hold the drag button down to prevent release of the button and termination of the drag sequence while accomplishing the multiple strokes. If the finger is simply lifted from the screen, the drag sequence will terminate and must again be started. Even if the cursor can be dragged with a single touchpad stroke, it is extremely difficult to maintain sufficient pressure on the touchpad to hold the button down while sliding the finger across the touchpad surface. Consequently, in using touchpad devices for dragging, the drag sequences are frequently unintentionally terminated.